Two-phase flow systems in which steam and water at relatively low pressure enter the system, flow together at supersonic speed and then leave the system, as water, flowing at subsonic speed at a pressure higher than that of either incoming component, have been known for over 115 years. In the past, such systems have been used to increase water pressure where steam is available. A classic use of such a system is to pump water into a boiler using live steam from the boiler.
Such known systems involve the use of supersonic steam flows which draw in water which enters the system. The two phase steam/water mixture enters an elongate flow tube in which the flow changes from supersonic to subsonic at a shock wave region where the pressure rises sharply. Downstream of the shock wave region there is generally a gap in the flow tube which is sometimes surrounded by a cavity having an egress opening for drainage.
As indicated in some of the references listed below, the gap/cavity/drainage system is used in the prior art systems during "start-up" to remove water which does not achieve the higher pressure which is achieved during operation.
Examples of such prior systems can be found in U.S. Pat. Nos. 177,313; 182,483; 209,220; 233,532; 280,589; 316,804; 338,950; 369,097; 440,488; 495,286; 501,271; 2,066,867; 4,252,572 and 4,951,713. Many of these patents are directed to the problems of start-up of the system and to its instabilities.
While such systems have been in use for many years, they were not well understood. Only in 1968 was a comprehensive theory of operation published by Deich, M. E. and Philippov, G. A. (in "Gas Dynamics of Two Phase systems," Moscow 1968, pp 267-274). This paper predicted that there is a theoretical limit to the amount of pressure step-up ratio which could be achieved, and that this limit was 5-7:1. In practice, commercially available supersonic injectors, such as the MIH-Jet models MBC-1 and MBC-2 manufactured by Jordan Equipment Co. of Houston, Tex., U.S.A. operate at pressure step up ratios between 2 and 2.5:1.
EP 0 150 171 describes a supersonic injector utilizing gas absorption in a supersonic liquid-gas mixture, resulting in a shock wave region.
SU 1281761 describes an injector which includes a supersonic steam injector opening into a mixing chamber followed by a flow tube. The inventor theorized that, for stable operation of injectors, it is necessary that the range of the ratio of the diameters of the outlet from the steam injector to the diameter of the flow tube be between 1.1-1.7:1 for highest possible pressure rise and for stable operation.
WO 89/10184, also published as EP 0 399 041, describes an emulsifier utilizing a passive injector. In this system steam, oil and water enter the system at separate entrances and exit the system as emulsified oil in water at an exit.
SU 1507299 describes a system in which a passive supersonic injector without a gap is used to pasteurize a liquid whole milk substitute.
U.S. Pat. No. 3,200,764 describes a passive injector in which a supersonic stream of steam is mixed with water, in a mixing region, to form a subsonic mixture of steam and water. This subsonic stream becomes supersonic in a gap following the mixer due to continued condensation of the and impinges a diffuser in which a diffused shock wave is generated. A spike, which protrudes from the diffuser, initiates the shock wave, which appears to extend over a substantial length.
EP 0 475 284 describes a system in which two fluids mixed at a supersonic speed. The mixture, is first made to flow at supersonic speed before entering a flow tube in which the flow becomes subsonic. This publication alleges that this results in an increase in pressure at the output of the system.